Flakes seen here:

https://ci.chromium.org/buildbot/tryserver.chromium.mac/mac_optional_gpu_tests_rel/19110
https://ci.chromium.org/buildbot/tryserver.chromium.mac/mac_optional_gpu_tests_rel/19084

In https://ci.chromium.org/buildbot/tryserver.chromium.mac/mac_optional_gpu_tests_rel/19084 the test failed:

  AssertionError: should be 0,0,255
  at (15, 1) expected: 0,0,255 was 0,255,255
  FAIL should be 0,0,255
  at (15, 1) expected: 0,0,255 was 0,255,255
  should be 0,0,255
  at (31, 1) expected: 0,0,255 was 0,255,255
  FAIL should be 0,0,255
  at (31, 1) expected: 0,0,255 was 0,255,255
  should be 0,0,255
  at (4, 16) expected: 0,0,255 was 0,255,255
  FAIL should be 0,0,255
  at (4, 16) expected: 0,0,255 was 0,255,255
  should be 0,0,255
  at (20, 16) expected: 0,0,255 was 0,255,255
  FAIL should be 0,0,255
  at (20, 16) expected: 0,0,255 was 0,255,255
  should be 0,0,255
  at (15, 1) expected: 0,0,255 was 0,255,255
  FAIL should be 0,0,255
  at (15, 1) expected: 0,0,255 was 0,255,255
  should be 0,0,255
  at (31, 1) expected: 0,0,255 was 0,255,255
  FAIL should be 0,0,255
  at (31, 1) expected: 0,0,255 was 0,255,255


In WebglConformance_conformance2_textures_canvas_sub_rectangle_tex_2d_rgb9_e5_rgb_float the test timed out:

https://chromium-swarm.appspot.com/task?id=3a833b2f39e3a510&refresh=10&show_raw=1

[9/137] gpu_tests.webgl_conformance_integration_test.WebGLConformanceIntegrationTest.WebglConformance_conformance2_textures_canvas_sub_rectangle_tex_2d_rgb9_e5_rgb_float failed unexpectedly 302.2095s:

...

    recv_strict at third_party/catapult/telemetry/third_party/websocket-client/websocket/_abnf.py:371
      bytes_ = self.recv(min(16384, shortage))
    _recv at third_party/catapult/telemetry/third_party/websocket-client/websocket/_core.py:427
      return recv(self.sock, bufsize)
    recv at third_party/catapult/telemetry/third_party/websocket-client/websocket/_socket.py:83
      raise WebSocketTimeoutException(message)
  TimeoutException: 


This test doesn't seem to use any asynchrony so it's unclear how it could intermittently time out.